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Understanding Magnesium (Mg2+) Uptake: Biological Roles, Transport Mechanisms, and QTL Analysis

This study explores the critical biological roles of magnesium (Mg2+) in plants, focusing on its importance as a cofactor in chlorophyll production and various enzymatic processes. We investigate the mechanisms of Mg2+ uptake and identify quantitative trait loci (QTLs) associated with magnesium transport. The research highlights the effects of Mg2+ deficiency, signs of stress, and the competition with aluminum toxicity. Using candidate gene analysis, we examine the significance of various transporter proteins in different cellular compartments, paving the way for future studies on enhancing Mg2+ uptake in challenging soil environments.

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Understanding Magnesium (Mg2+) Uptake: Biological Roles, Transport Mechanisms, and QTL Analysis

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  1. Mg2+ uptake QTLs Hannah Itell and Eric Sawyer

  2. Biological roles for Mg2+ • chlorophyll • common cofactor (RNA pol, kinases, ATPases, …) • most Mg2+ is not free in cytoplasm (ATP/nucleotide-chelated or in organelles) < 2 mM chlorophyll a

  3. Biological roles for Mg2+ • vacuole: 3-13 mM Mg2+ • highest [Mg2+]: thylakoid lumen (30-50 mM), but importers unknown! • Mg2+ uptake hindered by acidic soils • Mg2+ deficiency can lead to Al3+ toxicity; transporter competition chlorophyll a

  4. Signs of Mg2+ deficiency • chlorophyll breakdown • impaired sugarmobilization • reduced growth, particularly roots

  5. Mg2+ biochemistry • Cation channels • MGT • MHX • Slow activating vacuolar channels (SVs) • MGT5 • MGT10 and FACCs (G) Bose et al. (2011)

  6. 1. Mg2+ channels (plasma membrane) • Hyperpolarization-activated • Depolarization-activated • Voltage-independent • Cyclic nucleotide-activated • Non-selective ion channels • AtCNGC10 (A. thaliana): mediates Mg2+ mobilization through the plant

  7. 2. Mg2+ Carrier Proteins (MGTs) • Magnesium (Mg2+) Transport Family • AtMGT1, 5, 7a, 9, 10 • Vary in affinity and sensitivity to Al3+ Plasma Membrane Mitochondria Chloroplast

  8. Candidate gene BLAST results AtCNGC10 AtMGT family

  9. IGB QTL: 7,628,656 +/- 1 Mbp No hits :( C6 39,822,476 bp

  10. IGB Cation/Calcium Exchanger @ 39,717,422 Cation/H+ Exchanger @ 39,945,936 Cation/H+ Exchanger @ 39,950,514 Cation/H+ Antiporter @ 40,277,578 QTL: 40,141,039 +/- 1 Mbp C8 41,758,685 bp

  11. IGB Metallothionein-like protein @ 43,295,039 Golgi-assoc. cation binding protein Heavy metal transport/detoxification domain-containing protein @ 43,792,027 Calmodulin-like protein @ 43,857,726 Calcium transporting ATPase @ 43,882,735 Similar to AT1G07810 cation transporter Heavy metal transport/detoxification superfamily protein @ 44,678,689 QTL: 44,023,210 +/- 1 Mbp C5 46,902,585 bp

  12. IGB V-type proton ATPase subunit d2 @ 35,255,037 Caleosin-related family protein @ 35,570,359 Major facilitator superfamily protein @ 35,825,037 small solute transporter Heavy metal transport/detoxification superfamily protein @ 36,474,786 Cation transport regulator-like protein @ 36,606,567 QTL: 35,691,416 +/- 1 Mbp Vacuolar cation/proton exchanger @ 39,433,988 & 39,437,869 QTL: 39,973,848 +/- 1 Mbp V-type proton ATPase 16 kDa proteolipid subunit c1/c3/c5 @ 39,793,003 C7 48,366,697 bp Cation proton exchanger @ 39,509,003 Heavy metal transport/detoxification superfamily protein @ 40,122,906

  13. IGB Magnesium Transporter (Predicted) @ 39,807,316 Mitochondrial Carrier Protein @ 40,692,677 QTL: 40,219,218 +/- 1 Mbp C4 53,719,093 bp

  14. Conclusions • No candidate gene BLAST hits within 1 Mbp of QTL • CNGC10 and MGT family hit every QTL +/- 10 Mbp • IGB search within 1 Mbp of QTLs found • vacuolar pumps/transporters • heavy metal transporters (Al3+-Mg2+ antagonism?) • Ca2+, Mg2+, and general cation transporters and binding proteins

  15. References Bose, J. et al. 2010. Role of magnesium in alleviation of aluminium toxicity in plants. Journal of Experimental Botany62: 2251-2264. Hermans, C. et al. 2010. Systems analysis of the responses to long-term magnesium deficiency and restoration in Arabidopsis thaliana. New Phytologist 187: 132-144. Perez, V. et al. 2008. Homeostatic control of slow vacuolar channels by luminal cations and evaluation of the channel-mediated tonoplast Ca2+ fluxes in situ. Journal of Experimental Botany 59: 3845-3855.

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